D.c. circuit breaker device including one or more auxiliary anodes



Apnl 23, 1968 so BREITHQLTZ 3,379,929

D C. CIRCUIT BREAKER DEVICE INCLUDING ONE OR MORE AUXILIARY ANODES Filed May 25, 1966 Arronuzys United States Patent O 3,379,929 D.C. CIRCUIT BREAKER DEVICE INCLUDING ONE OR MORE AUXILIARY ANODES Bo Breitholtz, Vasteras, Sweden, assignor to Allmnna Svenska Elektrislra Aktiebolaget, Vasteras, Sweden, a Swedish corporation Filed May 25, 1966, Ser. No. 552,790

Claims priority, application Sweden, May 26, 1965,

6,918/ 65 3 Claims. (Cl. 315-59) When a circuit for high voltage direct current with great power is broken, completely different problems arise than when an alternating current circuit is broken. The DC circuit is strongly inductive due to the reactors necessary for direct current and the inductive energy generated in the circuit must be dissipated during the breaking. When gas or vacuum discharging tubes are used in which a discharge caused by the current can be controlled from a condition with low arc voltage drop to space charging condition with extremely high arc voltage drop to limit the current completely or partially, all or the most part of the breaking energy is to be developed in the discharging tube serving asa breaking chamber. When it is realized that it is a question of voltages of 100 kw. and currents of ka. it will immediately be seen that an enormous quantity of energy is developed during the breaking time. Even if the breaking t-ime is short, the anode will be subjected to such a powerful bombardment of high energy electrons that an undesirable temperature increase may take place in the anode. The temperature increase may ibe so high that such a powerful vaporization of the anode material arises that the impedance of the discharg-ing path sinks towards the end of the breaking interval due to vaporized anode material and this may mean that the intended limiting or breaking of the current does not take place, that is, that the breaking is not successful. Vaporization of the anode material also causes rapid destruction of the anode.

The above mentioned disadvantages are avoided with a device made in accordance with the present invention for circuit breakers for DC circuits having high voltages and great power, which device comprises a discharging tube with an electron-emitting cathode connected to the negative pole of the circuit, one anode and -at least one ring-shaped auxiliary electrode arranged in the discharge path between the anode and cathode, and resistors connected between the anode and the 'auxiliary electrode nearest the anode and also between the auxiliary elec- -trodes. The invention is characterized in that the discharging tube consists of a vacuum discharging tube or a gas discharging tube provided with devices for controlling the d-ischarge from a condition with low arc voltage drop to a space charging condition with high arc voltage dro-p and that the positive pole of the curcuit is connected to the auxiliary electrode situated nearest the cathode.

In FIGURE 1 of the `accompanying drawings the main principle of the invention is shown, while FIGURE 2 shows a device having three auxiliary electrodes.

The embodiment of the invention shown in FIGURE 1 consists of a discharging tube 1 with a cathode 2 connected to the negative pole of the current circuit, an anode 3 and a ring-shaped auxiliary electrode 4. The auxiliary electrode 4 is connected to the positive pole of the current circuit by means of a conductor 5. The anode 3 is connected to the same pole across a resistor 6. An electron stream emitted by the cathode is shown by the arrows 7.

The device operates in the following manner. The electrons emitted from the cathode 2 and forming the electron current through the discharging tube pass through the ring-shape auxiliary electrode 4, meet the anode 3 and 3,379,929 Patented Apr. 23, 1968 pass through the resistor 6. The voltage across the resistor generates an electric iield between the anode and the auxiliary electrode having such 'a direction that it has a retarding effect on the electrons in the electron current in the tube when they are between the anode and the auxiliary electrode. The decrease in the kinetic energy of the electrons resulting from this retarding is obtained intained instead as thermal energy in the resistor 6 generated by the current ilowing through the resistor. If the resistance R of the resistor is chosen so that R=V/I, where V is the voltage which accelerates the electrons and I is the current in the electron beam, the electrons will reach the anode without appreciable kinetic energy and will therefore not cause a heating of the anode. All electron energy is converted into heat in the resistor 6.

It', however, R is chosen so that R V/I no electrons will reach .the anode 3, all returning to the auxiliary electrode 4. However, if the resistance R is cho-sen so that R V/I the electrons will reach the anode with the kinetic energy e(V-Rl), which is converted to undesired heat in the anode.

From the above it will Ibe seen that if R is c-onstant an alteration in the electron accelerating voltage V and the current I will effect an alteration in the heating conditions as long as neither the voltage nor the current is altered in such a direction that the ratio between them is unchanged. 'Io achieve the least possible heating of the anode, even when the voltage -or current is altered, an embodiment according to FIGURE 2 may be used.

In this embodiment of the invention three auxiliary electrodes 8, 9 and 1() are inserted between the cathode 2 and the anode 3 in the discharge tube 1. The anode is connected to a point 1'1 across 'a resistor 12 and a rst auxiliary electrode 8 is also connected to this point. Between the connection point 11 and a second connection point 13 a resistor 14 is inserted and to this point a second auxiliary electrode 9 is connected. A third connection point 15 is connected to the plus pole of the current circuit and to the third auxiliary electrode 10. Furthermore a third resistor 16 is inserted between 13 and 15.

If the operating voltage through the device has such a value that the electron current flows through the third auxiliary electrode 10 and the voltage drop generated across the resistor 16 is just large enough for the kinetic energy of the electrons to be used up when they reach the second auxiliary electrode 9, the electrons will be caught by this. The electron current 7 will then change from the minus pole, through the auxiliary electrode 10 into the auxiliary electrode 9 and further through the resistor 16 to the plus pole. If the voltage increases the kinetic energy of the electrons will also increase so that the electron current at least partly passes through the auxiliary electrode 9 also and reaches the auxiliary electrode 8, so that the resistor 14 will also be connected in the current circuit. From this it is clear tha-t at an increase in acceleration volt-age more and more resistors will be connected in the current circuit so that its resistance varies according to the acceleration voltage.

Ii the acceleration volt-age is relatively constant, which can be achieved, for example by varying the electrode distance, but the current varies, :the heating of the anode can still be kept within reasonable bounds if the resistor 6 in FIGURE 1 or the resistors 12, 14, 16 in FIGURE 2 are of non-linear type. This means that the induced retardation voltage between the auxiliary electrodes will to a great extent be independent of the current value.

The number of ring-shaped auxiliary electrodes is not limited to one or three, but may be determined according to the -conditions from case to case. Further, the shown and described embodiment-s may be complemented by means for varying the electrode distance to compensate for variations in voltage.

I claim:

1. Circuit breaker device for a DC circuit having high voltage and great power, which device comprises a discharging tube with an electron-emitting cathode connected to the negative pole of the circuit, one anode and at least one ring-shaped auxiliary electrode arranged in the discharge path between anode and cathode, and -a resistor connected between lthe anode and the auxiliary electrode, the positive pole of the circuit being connected to the -auxiliary electrode.

2. In a device as claimed in claim 1, said resistor being nQn-iinear.

3. Circuit breaker device for a DC circuit having high voltage and great power, which device comprises a discharging tube with an electron-emitting cathode connected to the negative pole of the circuit, one anode and a plurality of ring-shaped auxiliary electrodes arranged in the discharge path between anode and cathode at different distances from the cathode, a first resistor connected between the cathode and -the auxiliary electrode nearest the anode and second resistors between successive auxiliary electrodes, the posi-tive pole of the circuit being connected to the auxiliary electrode located nearest the cathode.

References Cited UNITED STATES PATENTS 2,235,497 3/1941 Heil 328--256 X JAMES W. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner. 

1. CIRCUIT BREAKER DEVICE FOR A DC CIRCUIT HAVING HIGH VOLTAGE AND GREAT POWER, WHICH DEVICE COMPRISES A DISCHARGING TUBE WITH AN ELECTRON-EMITTING CATHODE CONNECTED TO THE NEGATIVE POLE OF THE CIRCUIT, ONE ANODE AND AT LEAST ONE RING-SHAPED AUXILIARY ELECTRODE ARRANGED IN THE DIS- 